1 Technical Field
This disclosure relates generally to a relay system equipped with a pair of main switches and a control circuit working to control on-off operations of the main switches.
2 Background Art
Japanese Patent First Publication No, 2012-152071 discloses a relay system equipped with a pair of power lines, main switches, a capacitor, and a control circuit. The power lines connect between a do power supply and an electrical device. The main switches are disposed in the power lines, respectively. The capacitor is connected between the power lines. The control circuit works to control on-off operations of the main switches. The relay system also has a series-connected assembly of a current-limiting resistor and a pre-charge switch. The series-connected assembly is connected in parallel to one of the main switches. The control circuit works to control on-off operations of the main switches and the pre-charge switch.
The main switches are disposed in a relay module along with a main coil and a sub-coil. The relay module is engineered to turn on both the main switches when only the main coil is energized and turn on only one of the main switches to which the series-connected assembly is not joined when the main and sub-coils are both energized.
The control circuit turns on or off the main switches and the pre-charge switch to switch among a power-off mode, a pre-charge mode, and a power-on mode. In the power-off mode, the control circuit turns off the main switches to stop supply of electric power from the dc power supply to the electrical device. In the pre-charge mode, the control circuit turns on the pre-charge switch and energizes the main and sub-coils to turn on one of the main switches to which the series-connected assembly is joined in parallel, while turning off the other main switches to which the series-connected assembly is not joined, thereby causing electric current to flow to the capacitor through the current-limiting resistor to charge the capacitor gradually. After the capacitor is charged, the control circuit enters the power-on mode in which only the main coil is energized to turn on both the main switches, thereby starting delivering the power from the do power supply to the electrical device.
As described above, the relay system turns on both the main switches after the capacitor is charged. This eliminates the risk that the main switches are both turned on when the capacitor is not yet charged, thus resulting in flow of inrush current to the capacitor.
The relay system is, as described above, designed to energize both the main and sub-coils in the pre-charge mode and alternatively energize only the main coil in the power-on mode. The supply of power to the electrical device is, therefore, maintained only by energizing the main coil, thereby reducing the amount of power consumed by the coils in the power-on mode.
The relay system, however, encounters the drawback in that when the sub-coil has malfunctioned, it may cause the main switches to be both turned on in the pre-charge mode, so that the inrush current flows to the capacitor. Specifically, in the pre-charge mode, the main and sub-coils are usually energized. If, therefore, the sub-coil has failed, only the main coil will be energized, so that the power-on mode, not the pre-charge mode will be entered. Therefore, the capacitor is not charged fully, but the main switches are both turned on, which may cause the inrush current to flow to the capacitor.